1. Field of the Invention
The present invention relates to a light source unit having a luminescent plate which becomes luminous based on energy from an excitation light source and a projector which includes the light source unit.
2. Description of the Related Art
In these days, data projectors are used on many occasions as image projection apparatuses which project images including images of screens and video images of personal computers, as well as images based on image data which is stored in memory cards on to a screen. In projectors of the type described above, conventionally, projectors using a high-intensity discharge lamp as a light source have been the mainstream of projectors. However, in recent years, there have been made many developments and proposals on projectors which use, as a light source, alight emitting diode (LED), a laser emitter, a device utilizing organic EL technology or luminescent materials.
For example, Japanese Unexamined Patent Publication No. 2004-341105 (JP-A-2004-341105) proposes a light source unit in which red, green and blue luminescent material layers are laid end to end on a surface of a luminescent plate made up of a light transmissive circular plate and a dichroic filter which transmits ultraviolet light and reflects visible light is disposed on a back side of the luminescent plate and which generates a light-source light of red wavelength band, a light-source light of green wavelength band and a light-source light of blue wavelength band by shining ultraviolet light onto the luminescent material layers from the back side of the luminescent plate.
As has been described above, there exist projectors which utilize, as a light-source light, luminescent light emitted from a luminescent material of a luminescent material layer by shining light emitted from an excitation light source to the luminescent material layer. In these projectors, the quantity of luminescent light emitted from the luminescent material of the luminescent material layer can be increased by increasing the output of the excitation light source. However, when a laser emitter is used as an excitation light source, in the event that the power of a laser beam emitted from the laser emitter is increased, there has been caused a fear that the luminance saturation of the luminescent material or a failure thereof attributed to scorching is generated.
On the other hand, when a laser beam is shone onto the luminescent material layer while being diffused to weaken the power per unit area of the laser beam with the power of the laser bean being increased, the area illuminated by the laser beam gets wider than the area of the portion of the luminescent material layer that is to be illuminated by the laser beam, whereby the laser beam is shone onto positions which lie out of the luminescent material layer, leading to a problem that the utilization efficiency of light emitted from the laser emitter is decreased.